Method and pump unit for a pressure sewerage system

ABSTRACT

A pump unit for a pressure sewage system, including a pump for insertion in a sewage holding tank, the pump being capable of activation for pumping sewage out of the holding tank to an external pipeline, and a timer unit enabling activation of the pump for a first predetermined time period and preventing activation of the pump for a second predetermined time period directly following the first time period.

FIELD OF THE INVENTION

The present invention relates to pump units in pressure sewerage systemsand methods of operation.

BACKGROUND OF THE INVENTION

Pressure sewerage systems are used in areas where the cost of tanks,pumps, pressure pipelines and pumping of sewage is less than the cost ofthe larger, deeper sewers required for conventional gravity seweragesystems. Individual pump systems are provided for each property, witheach system pumping into a common pressure pipeline. They areparticularly suitable where conventional gravity systems are prejudicedby localised topography, geology and/or environmental and socialconditions.

Current pump systems include an underground upright tank in which a pumpis mounted. The tank located in each property receives sewage from thatproperty and when the tank fills to an ‘on’ level, the pump is activatedto pump the sewage from the tank to a common pressure pipeline to whicheach of the properties along a street is connected. The pump remainsactive until the level of sewage in the tank goes down to an ‘off’ levelwithin the tank.

The spacing of the ‘on’ and ‘off’ levels is traditionally determined asa function of a maximum number of pump starts per hour. A typicalhousehold produces about 600 litres per day of sewage. For a tank ofmaximum volume of 667 litres, the spacing would typically align to 189litres between the ‘on’ and ‘off’ levels. These pumps typically pumpabout 0.5 litres per second and can include an over-pressure cut-outfeature, which stops the pump if the pressure at its outlet exceeds acertain threshold. This feature protects the pump motors in the adventof pipeline blockage or hydraulic overloading of the pressure systemwhen too many pumps attempt to start simultaneously in peak flow periodsand particularly after an extended power failure.

The volume in the tank above the ‘on’ level is provided for emergencystorage in the advent of extended power failure as well as temporarilystoring abnormal peak flows of sewage such as when water is releasedfrom a full spa bath. The amount of water below the ‘off’ level istypically a simple function of the geometry of the pump and the tank, asmost pumps are placed in the bottom of standard tanks without specificconsideration to the use of the tank. The amount below the ‘off’ levelcan be 65 litres, which can lead to deposits on the base of the tank.

There are inherent conflicting design requirements for sizing of thestreet pressure main pipelines. On one hand these pipelines must be aslarge as possible to minimise pumping costs and overflow risks, allowsimultaneous operation of as many pumps as possible during peak flowperiods and post power outage recovery. On the other hand they must beas small as possible to minimise cost and sewage age. Compromisesinvariably do not favour sewage age considerations.

A key problem with current pressure sewerage systems include significanthydrogen sulphide generating with resultant odour (a rotten egg odour),causing OH&S and pipe corrosion risks in the pump unit itself, and alsoin the pressure pipeline and in the downstream receiving seweragesystem. This arises because the average age of the sewage leaving aproperty is commonly more than 12 hours. Age dependent septicity onsetis dependent on many factors including climate, nature of the sewage,sewage temperature, trade wastes, groundwater and topography. InVictoria, Australia, for example, septicity onset of sewage commonlyoccurs at an age of around 6 to 9 hours. Compromised street pressurepipelines invariably add sewage age to the point where septic dischargesto the downstream sewerage system are unavoidable. Septic sediments thataccumulate in a tank cause acceleration in the septicity of freshsewage.

Another key problem with current pressure sewage systems is that duringa power failure, the tanks of all of the properties in a street can fillup, or even overflow during extended power failures, such as those over24 hours. When the power supply reactivates, all of the pumps wouldattempt to commence operation simultaneously. This results in thepressure within the common pipeline along the street exceeding the pumpcut-out threshold, so that the pumps of the upstream properties remaininactive for an extended period of time until the pumps of thedownstream properties have emptied their tanks to their respective ‘off’levels and stopped pumping. This in turn means that the downstream unitsreturn to normal operation relatively quickly, whilst the upstream unitsmight remain inactive for up to 36 hours or so leading to increasedoverflow risks from those tanks, as well as increased localised odourrisks from increased sewage age.

It is therefore a desired object of the invention to provide analternate pump unit for pressure sewerage systems that overcomes, or atleast minimises, at least one of the problems associated with currentsystems, or at least provides an alternative solution.

Reference to any prior art in the specification is not, and should notbe taken as, an acknowledgment or any form of suggestion that this priorart forms part of the common general knowledge in Australia or any otherjurisdiction or that this prior art could reasonably be expected to beascertained, understood and regarded as relevant by a person skilled inthe art.

SUMMARY OF THE INVENTION

The present invention provides a timer unit for controlling a pump for apressure sewage system, the timer unit enabling activation of the pumpfor a first predetermined time period and preventing activation of thepump for a second predetermined time period directly following the firsttime period.

According to a first aspect, the present invention provides a pump unitfor a pressure sewage system, including:

-   -   a pump for insertion in a sewage holding tank, the pump being        capable of activation for pumping sewage out of the holding tank        to an external pipeline;    -   a timer unit enabling activation of the pump for a first        predetermined time period and preventing activation of the pump        for a second predetermined time period directly following the        first time period.

Preferably, the pump unit is provided as a kit. The timer unit may beprovided as part of a controller unit. The timer unit is preferablyprogrammed to send start and stop signals to the pump controller.

According to a second aspect, the present invention provides a sewagepump arrangement for a pressure sewage system, including:

-   -   a holding tank for receiving and temporarily holding sewage from        a building;    -   a pump housed in the tank, the pump being capable of activation        for pumping sewage out of the holding tank to an external        pipeline;    -   a timer unit enabling activation of the pump for a first        predetermined time period and preventing activation of the pump        for a second predetermined time period directly following the        first time period.

According to a third aspect, the present invention provides a pressuresewage system, including:

-   -   a plurality of holding tanks at spaced locations connected to a        common sewage pipeline; and    -   each holding tank including a pump unit according to the first        aspect of the present invention.

Preferably, the pump is activated by a switch triggered when the sewagein the tank reaches a first predetermined level. The pump is deactivatedby either a switch triggered when the sewage in the tank reaches asecond predetermined level below said first level, or when the firstpredetermined time period ends, whichever occurs earlier. Once thesecond predetermined time period ends, if the activation switch is stilltriggered, the pump will be activated. The first predetermined timeperiod may be, for example, 30 seconds and the second predetermined timeperiod may be 9 minutes and 30 seconds, whereby each individual sewagepump arrangement is capable of pumping sewage into the common pipelinefor 30 seconds every 10 minutes.

The activation and deactivation switches may be a level control device,such as a float switch, multi-trode, ultrasonic switch or other.

Advantageously, the timer unit is independently powered.

Preferably, the internal diameter of the bottom section of the tank isless than the upper section of the tank. The bottom section of the tankmay be stepped into a smaller diameter or may be downwardly tapered. Thevolume of sewage held between the pump activation level and the pumpdeactivation level is preferably less than 20 litres, more preferablybeing 10 litres. Alternatively, a conical insert can be provided, thatis inserted into the base of a standard shaped tank, lessening thevolume of the base of the tank, therefore shortening the durationbetween activations of the pump.

Preferably, each pump includes an over-pressure cut-out device, such asa pressure switch or thermal overload, which stops the pump fromactivating if the pressure at the outlet exceeds a set threshold or isnear pump shut-off head.

According to a fourth aspect, the present invention provides a method ofcontrolling a pressure sewage system, including:

-   -   providing each of a plurality of spaced buildings with:        -   a holding tank for receiving and temporarily holding sewage            from a building;        -   a pump housed in the tank, the pump being capable of            activation for pumping sewage out of the holding tank to an            external pipeline;        -   a timer unit in communication with a pump controller;        -   an over-pressure cut-out device for preventing activation of            the pump when the pressure at the outlet exceed a set            threshold;    -   wherein the timer units enable activation of the respective        pumps for a first predetermined time period and prevent        activation of the respective pumps for a second predetermined        time period directly following the first time period, whereby        the over-pressure cut-out device prevents simultaneous        activation of a predetermined number of pumps, and the timer        units allow for the random activation of the plurality of pumps.

According to an embodiment, the controller units of the plurality ofspaced holding tanks could be in communication with a central monitoringsystem, whereby an over-riding shut off message could be sent toindividual pump units or a plurality of pump units.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of a common sewage pipelinesystem for several properties in a street, each having a holding tankfor sewage;

FIG. 2 is a perspective view of a holding tank according to a firstembodiment of the present invention;

FIG. 3 is a cross-sectional side view of a sewage pump arrangementincluding the holding tank of FIG. 2; and

FIG. 4 is a cross-sectional side view of a sewage pump arrangementaccording to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As shown in FIG. 1, a pressure sewage system 10 includes a commonpipeline 12 to which a number of properties 14 are connected. Thebuildings 16 on each property 14 feed sewage via conventional gravityhouse drains via conduits 18 into holding tanks 20, which are typicallyat least partially buried below ground surface. The holding tanks 20 areconnected to the common pipeline 12 via small diameter pressure conduits22.

Holding tanks 20 (FIG. 2) are generally cylindrical with an upright wall24. The tank 20 has an upper opening 28, which provides access to theinside of the tank and would be closed by a manhole cover (not shown).The bottom section 30 of the tank 20 includes an insert 35 providing astep at 34 such that the diameter is less in the bottom section 30 thanin the upper section 32, whereby the bottom section 30 holds arelatively small volume of fluid, being less than 50 litres, butpreferably 15 litres, below the step 34. Step 34 is inclined at about1:1 slope (a 45 degree angle) so as to prevent sediment retention. Theconical insert 35 is inserted into a standard shaped tank 20. Thisprovides a high structural integrity for the base. The cavity 37 formedbeneath the conical insert can be filled with concrete to weigh down thebase. This would prevent floatation of the tank, which readily occursduring extremely wet weather periods. As shown in FIG. 4, rather than aconical insert, the bottom of the tank 21 could be stepped at 34.

The tank 20 includes a number of inlets 36, being an opening positionedjust above the step 34. The inlet 36 connects to conduit 18. A flat base38 is provided on which sits a pump 40, which can be activated to pumpsewage from the bottom of the tank through pipe 42 to outlet 44positioned near the top of wall 24, to connect up with conduit 22 whichconnects to the common pipeline 12.

A controller unit 48 with various sensing arrangements within the tank,such as float switch 46, controls the activation and deactivation of thepump. An override timer unit 50 is provided within the pump that isprogrammed to send start and stop signals to the controller unit 48,which controls the duration of the pump activation, only allowing thepump to operate periodically. The timer unit in the embodiment shown isintegrated into the controller unit. The timer unit allows theactivation of the pump for a first predetermined time period, such as 30seconds, and then sends a stop signal to prevent activation of the pumpfor a second predetermined time period, such as 9 minutes and 30seconds, directly following the first time period. At the end of thesecond time period a start signal is sent, with the stop signal onlybeing sent once the pump has activated again for a period of 30 seconds.

The activation of the pump 40 is by float switch 46 that is located inthe bottom section 30 of the tank. As the tank 20 fills with sewage, thefloat switch 46 is raised to the top of the bottom section, generallyaligning with the step 34. Once it reaches an upper predetermined ‘on’level 50, the pump is triggered to activate. If the timer unit is notwithin the second predetermined time period, then the pump will beallowed to activate to pump the sewage out of the pump. The pump willthen stop when either the float switch 46 reaches a lower predetermined‘off’ level 52, or when the first predetermined time period has ended,whichever occurs first. If the float switch 46 is raised to the upperpredetermined ‘on’ level 50, whilst the timer unit is within the secondpredetermined time period, then the pump will be prevented fromactivating until the second predetermined time period has ended and thetimer unit has sent a start signal to the controller.

The reduced volume in the bottom section 30 means that the volume offluid between the upper ‘on’ level 50 and lower ‘off’ level 52 isreduced from around 190 litres to 10 litres (one toilet flush), thus thetank operates for shorter periods more frequently. This can result insewage being held in the tank for up to 3 hours, as opposed to 10 hoursin current systems. Sewage can turn septic after 6 to 9 hours. Thecombination of minimising retained sewage below the lower ‘off’ level 52and the flat sloping surface of the step 34 avoids or at least minimises“dead” pockets which can accumulate sediment. Whilst the temporarystorage volume has decreased, the overall storage volume of the tank isnot reduced greatly, such that it is still able to hold sufficientamounts as required during a power failure or extreme weatherconditions. The configuration of the system provides additional bufferstorage of around 200 litres above the upper ‘on’ level 50, at step 34,and the inlet pipe 36. An alarm system can be provided that indicateswhen the tank has reached a level near the top of the tank; this canalso occur when the pump fails.

Each pump includes an over-pressure cut-out, which additionally stopsthe pump from activating if the pressure at the outlet exceeds a setthreshold.

The pump 40 is only allowed to pump sewage out of the tank 20 when thelevel of sewage is at or above a certain height, being the upper ‘on’level 50, and when the timer is in the first predetermined time period.In effect the timer unit is an over-riding two way switch.

According to this approach, after a power failure the reactivation ofthe pumps of system 10 is not correlated in the traditional way, as thestarting of the pumps is randomised so that the upstream pump unitsreturn to operational state at a similar time to the downstream units.As the pump units are each allowed to run for shorter periods, eachwould in effect take it in turns to empty part of their tanks, ratherthan the upstream tanks having to wait until the downstream tanks werefully emptied. By controlling the pumping periods and discharges foreach pump unit, the amount of time that pumps operate simultaneously isreduced, leading to a reduction in peak flows and sewage age throughoutthe common system.

The timer unit 50 is powered independently, such that the timer unitsare not reset by a power failure. Random pump operation is maintained inthe advent of a power failure as timer settings are frozen and uponpower resumption, settings resume and are not reset to zero. This meansthat after a power failure all of the pumps in a system do not commenceoperation simultaneously.

The timer unit 50 and the pump 40, which would include the controllerunit, could be provided as a kit for insertion into an existing tank 20.Alternatively, a sewage pump arrangement could be provided, where thetimer unit and pump are provided with a tank.

The present invention thereby reduces the likelihood of tanks turningseptic. The present invention also attenuates peak flows which allowssmaller street pressure mains; it is thought that the advantages aresufficient such that a smaller common pipeline down the street, abouthalf the size of conventional, can be used thus leading to a significantcost saving, whilst also significantly reducing the problems associatedwith sulphides. This greatly reduces the impact on the downstreamsewerage system and means that existing sewerage systems can be expandedto include new areas, as the existing sewerage system could be adaptedto accommodate, rather than having to create all new sewerage systemsfor new areas, as is currently required when a sewerage system is atmaximum capacity.

It will also be appreciated that the systems could be configured tocommunicate with the Smart Meters, which are being introduced toproperties to measure the flow rate of individual properties. The SmartMeters could be used to communicate back to a centralized monitoringpoint, where individual pump units or a number of properties could beshut down through their timer unit, when there was an overload on thedownstream sewerage system, or when repair work was required on thesewerage system of common pipeline.

It will be understood that the invention disclosed and defined in thisspecification extends to all alternative combinations of two or more ofthe individual features mentioned or evident from the text or drawings.All of these different combinations constitute various alternativeaspects of the invention.

1. A pump unit for a pressure sewage system, including; a pump forinsertion in a sewage holding tank, the pump being capable of activationfor pumping sewage out of the holding tank to an external pipeline; atimer unit enabling activation of the pump for a first predeterminedtime period and preventing activation of the pump for a secondpredetermined time period directly following the first time period.
 2. Apump unit according to claim 1, wherein the pump unit is provided as akit.
 3. A pump unit according to claim 1, wherein the timer unit isprovided as part of a controller unit that controls activation of thepump.
 4. A pump unit according to claim 3, wherein the timer unit isprogrammed to send start and stop signals to the controller unit.
 5. Apump unit according to claim 1, wherein the pump is activated by aswitch triggered when the sewage in the tank reaches a firstpredetermined level.
 6. A pump unit according to claim 5, wherein thepump is deactivated by either a switch triggered when the sewage in thetank reaches a second predetermined level below said first level, orwhen the first predetermined time period ends, whichever occurs earlier.7. A pump unit according to claim 6, wherein, once the secondpredetermined time period ends, if the activation switch is stilltriggered, the pump will be activated.
 8. A pump unit according to claim1, wherein the first predetermined time period is less than 60 secondsand the second predetermined time period is less than 10 minutes.
 9. Apump unit according to claim 5, wherein the activation and deactivationswitches are level control devices, such as a float switch.
 10. A pumpunit according to claim 1, wherein the timer unit is independentlypowered.
 11. A pump unit according to claim 1, wherein the pump includesan over-pressure cut-out device, which stops the pump from activating ifthe pressure at the outlet exceeds a set threshold.
 12. A sewage pumparrangement for a pressure sewage system, including: a holding tank forreceiving and temporarily holding sewage from a building; a pump housedin the tank, the pump being capable of activation for pumping sewage outof the holding tank to an external pipeline; a timer unit enablingactivation of the pump for a first predetermined time period andpreventing activation of the pump for a second predetermined time perioddirectly following the first time period.
 13. A sewage pump arrangementaccording to claim 12, wherein the internal diameter of the bottomsection of the tank is less than the upper section of the tank.
 14. Asewage pump arrangement according to claim 13, wherein the bottomsection of the tank is stepped into a smaller diameter, and isdownwardly tapered.
 15. A sewage pump arrangement according to claim 12,wherein the volume of sewage capable of being held between the pumpactivation level and the pump deactivation level is preferably less than20 litres.
 16. A sewage pump arrangement according to claim 15, whereinthe volume is 10 litres.
 17. A sewage pump arrangement according toclaim 12, wherein the timer unit is provided as part of a controllerunit that controls activation of the pump.
 18. A sewage pump arrangementaccording to claim 17, wherein the timer unit is programmed to sendstart and stop signals to the controller unit.
 19. A sewage pumparrangement according to claim 12, wherein the pump is activated by aswitch triggered when the sewage in the tank reaches a firstpredetermined level.
 20. A sewage pump arrangement according to claim19, wherein the pump is deactivated by either a switch triggered whenthe sewage in the tank reaches a second predetermined level below saidfirst level, or when the first predetermined time period ends, whicheveroccurs earlier.
 21. A sewage pump arrangement according to claim 20,wherein, once the second predetermined time period ends, if theactivation switch is still triggered, the pump will be activated.
 22. Asewage pump arrangement according to claim 12, wherein the firstpredetermined time period is less than 60 seconds and the secondpredetermined time period is less than 10 minutes.
 23. A sewage pumparrangement according to claim 19, wherein the activation anddeactivation switches are level control devices, such as a float switch.24. A sewage pump arrangement according to claim 12, wherein the timerunit is independently powered.
 25. A sewage pump arrangement accordingto claim 12, wherein the pump includes an over-pressure cut-out device,which stops the pump from activating if the pressure at the outletexceeds a set threshold.
 26. A pressure sewage system, including: aplurality of holding tanks at spaced locations connected to a commonsewage pipeline; and each holding tank including a pump unit accordingto claim
 1. 27. A method of controlling a pressure sewage system,including: providing each of a plurality of spaced buildings with: aholding tank for receiving and temporarily holding sewage from abuilding; a pump housed in the tank, the pump being capable ofactivation for pumping sewage out of the holding tank to an externalpipeline; a timer unit in communication with the pump; an over-pressurecut-out device for preventing activation of the pump when the pressureat the outlet exceed a set threshold; wherein the timer units enableactivation of the respective pumps for a first predetermined time periodand prevent activation of the respective pumps for a secondpredetermined time period directly following the first time period,whereby the over-pressure cut-out device prevents simultaneousactivation of a predetermined number of pumps, and the timer units allowfor the random activation of the plurality of pumps.